Speed endurance the key to *all* 11/12second sprinters?

Can be. Let’s say the athlete is running 100, 200, 4 x 100 on the weekend. You might do 2 x 150 or maybe 1 x 250 (depending on the athlete) sub max on Tues and a few starts Thurs with the rest being tempo and med ball/conditioning etc. The primary advancement of SE abilities of course is coming from the meets.